Method

ABSTRACT

The present invention relates to new and improved methods of synthesizing radiolabelling agents which can be used to label biomolecules for use as radiopharmaceuticals. It further relates to certain novel radiolabelling agents and their use in such methods. PET imaging methods and methods of diagnosis employing such radiolabelling agents form a further aspect of the invention.

The present invention relates to new and improved methods ofsynthesizing radiolabelling agents which can be used to labelbiomolecules for use as radiopharmaceuticals. It further relates tocertain novel radiolabelling agents and their use in such methods.

The method of the invention is simpler, faster and higher yielding thanconventional methods for preparing radiolabelling agents, can be carriedout at room temperature, and does not require a phase-transfer catalyst.The radiolabelled compounds produced by the method find particular useas labelling agents (prosthetic groups), for example in theradiolabelling of biomolecules or other molecules which cannot belabelled directly (or can only be labelled in poor yield) bynucleophilic addition of a radionuclide or which otherwise require theuse of reaction mixtures which do not allow easy separation of thelabelled product and nonlabelled biomolecule. Radiolabelled compoundsobtained by the method of the invention and biomolecules labelled withsuch compounds find particular application as tracers in positronemission tomography (PET). Advantageously, the method of the inventioncan be performed on existing commercial PET synthesizer platforms.

PET is an imaging modality increasingly used in nuclear medicine.Fluorine-18 (¹⁸F) has near-ideal properties for PET imaging due to itshalf-life of 110 minutes, high positron abundance (97%), low positronenergy (0.634 MeV) and its high production efficiency using a cyclotron.

2-[¹⁸F]fluoro-2-deoxy-D-glucose (FDG) is by far the most-used ¹⁸F PETtracer in a clinical setting. However, there are several indicationswhere FDG shows no utility or has low impact on clinical management.Other tracers are therefore needed to fill this void. One class oftracers is based on biomolecules (e.g. peptides, peptidomimetics,affibodies, diabodies, nanobodies, dendrimers, aptamers, antibodies,antibody mimetics and proteins). This class of tracers is increasinglyfinding use in nuclear medicine. Peptides and other biomolecules areexcellent targeting probes (tracers) for PET due to their highspecificity. Their biological pharmacokinetics are also well-matched tothe radioactive half-life of ¹⁸F, especially in the case of peptides andpeptidomimetics. Examples of such tracers include prostate specificantigen membrane antigen (PSMA) somatostatin analogues and chemokinereceptor targeting probes. Examples of biomolecule-based tracers aredescribed in Chen et al., Clinical Cancer Research, 17(24): 7645-53,(2011); and in Greguric et al., Journal of Medicinal Chemistry, 52:5299-5302 (2009).

The chemistry of ¹⁸F in relation to biomolecules is hampered by theharsh conditions required to form a covalent bond of ¹⁸F to thebiomolecule. As a consequence, ¹⁸F is normally introduced intobiomolecules using an ¹⁸F-prosthetic group. Several ¹⁸F-based prostheticgroups have been described in the literature. However, these suffer fromcomplicated multi-step synthetic routes and protracted synthesis times,often 90 minutes or more. This has hindered the widespread use of¹⁸F-labelled biomolecules in PET. Instead, there is increasing clinicaluse of ⁶⁸Ga-labelled peptides such as [⁶⁸Ga]DOTATOC and [68Ga]PSMA,despite the fact that ⁶⁸Ga is costlier to produce and has a sub-optimalhalf-life and sub-optimal imaging properties compared to ¹⁸F.

To allow a more widespread clinical use of ¹⁸F-based biomolecules, asimplified and high-yielding process for their production is required.This in turn requires a simpler, more cost-effective process forproducing the required ¹⁸F-prosthetic groups in high yield.

An ¹⁸F-prosthetic group suitable for labelling biomolecules is[¹⁸F]fluoronicotinic acid 2,3,5,6-tetrafluorophenyl ester (abbreviatedas [¹⁸F]F-Py-TFP). This has the following structure:

[¹⁸F]F-Py-TFP can be synthesised by reacting [¹⁸F]fluoride with theprecursorN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate:

[¹⁸F]F-Py-TFP and its synthesis fromN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate are described in WO 2010/114723 and in Olberget al., Journal of Medicinal Chemistry, 53, 1732-1740 (2010), thecontents of which are incorporated herein by reference.

[¹⁸F]F-Py-TFP is an active ester and forms stable amide bonds with aminefunctionalities found in many biomolecules. Additionally, the[¹⁸F]fluoropyridine moiety that is incorporated into the biomolecule hasa low lipophilic impact on the biomolecule thus favouring renalexcretion and low unspecific binding of the PET tracer.

The conventional synthesis of [¹⁸F]F-Py-TFP, as described in WO2010/114723 and Olberg et al., is based on the following steps:

1. Preparation of the Fluorinating Agent:

The radionuclide (¹⁸F) is produced in advance by irradiation of ¹⁸Oenriched water with a proton beam produced in a particle accelerator,giving ¹⁸F⁻ or H¹⁸F in an aqueous solution. The radionuclide-containingsolution is then passed through a column containing a solid-phasesupport (typically an anion-exchange resin) which traps the[¹⁸F]fluoride in the column.

The ¹⁸F anion is activated by eluting the trapped [¹⁸F]fluoride from theanion-exchange resin into a reaction vessel. The elution is accomplishedusing a phase transfer catalyst (PTC) such as tetrabutylammoniumbicarbonate (TBA-HCO₃). It is of major importance that the elutionsolution (i.e. the solution containing the phase transfer agent oragents) is alkaline to render the fluoride nucleophilic, and to minimizeevaporation of H¹⁸F gas in the following step.

2. Labelling of the Precursor:

The fluorinating agent (i.e. [¹⁸F]fluoride) is made anhydrous bysubsequent additions of acetonitrile (CH₃CN) to the reaction vessel andevaporation using heat (90 to 100° C.) and a sweep gas (N₂ or He). Aftercooling of the reaction vessel to 40° C., the precursorN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate dissolved in 1 mL of a 1:1 mixture ofacetonitrile and tert-butyl alcohol is then added to the dry TBA-¹⁸Fresidue. An aromatic nucleophilic substitution reaction in which theN,N,N-trimethylaminium of the precursor is displaced by the ¹⁸F atom,results in the formation of [¹⁸F]fluoronicotinic acid2,3,5,6-tetrafluorophenyl ester ([¹⁸F]F-Py-TFP). This reaction normallytakes 10 minutes. The true incorporation yields of 18F are around50-60%, due to decomposition of the precursor and sticking of fluorideto the reaction vessel, as described in Olberg et al.

This conventional procedure has, however, a number of drawbacks,including but not limited to the following:

-   -   The overall duration of the process is at least 20 minutes,        mainly due to the number of successive drying steps needed to        render the ¹⁸F anhydrous and subsequent cooling of the reaction        vessel prior to the addition of fluoride.    -   Most commercial PET synthesizer platforms are only equipped with        a single reaction vessel. This will be contaminated for the next        synthesis step where [¹⁸F]F-Py-TFP is reacted with the        biomolecule in question. This makes it challenging to        accommodate a full ¹⁸F-biomolecule preparation process using the        above-described procedure on an automated commercial platform.    -   The need for a phase-transfer-catalyst necessitates a limit test        for its presence in the final drug product—a time-consuming        quality control test that allows ¹⁸F to decay further before        product release.    -   The use of a weak base such as HCO₃ ⁻ during elution makes the        fluoride more prone to irreversible adsorption to the vessel        wall making it unavailable for reaction with the precursor.

It is therefore desirable to provide an improved, e.g. a simpler andfaster, process for the preparation of ¹⁸F-labelled compounds such as[¹⁸F]F-Py-TFP which overcomes these drawbacks.

In recent years there has been increasing interest in so-called“on-column” or “solid phase” radiofluorination. In such methods the[¹⁸F] fluoride is not eluted from the column for subsequent reactionwith a precursor (prosthetic group) in a reaction vessel. Instead, theprecursor and the [¹⁸F]fluoride undergo reaction on the column itself,i.e. in-situ. However, “on-column” radiofluorination processes reportedso far in the literature suffer from poor yield and also have otherdrawbacks such as requiring significant heating in order to activate the¹⁸F anion sufficiently to attain a reaction rate suitable for PETradiopharmaceutical manufacture. Mathiessen et al. (Molecules 2013, 18,10531-10547) have recently reported on-column ¹⁸F labelling of smallmolecules using custom-made resins. However, this work suffered from atedious process taking about 35-45 minutes, poor yields, and the needfor elevated column temperatures. On-column methods of ¹⁸Fradiolabelling have therefore so far not found commercial use.

The invention provides an alternative process for on-columnradiofluorination in order to provide ¹⁸F-labelled compounds for use asprosthetic groups in the radiolabelling of biomolecules. Morespecifically, it provides an improved on-column radiofluorinationprocess, e.g. one which is simpler, faster, and/or higher-yielding thanthose conventionally known in the art.

As employed herein, the term [¹⁸F]fluoride, equivalently [¹⁸F]F⁻, refersto a fluoride anion (F⁻) in which the fluorine isotope is fluorine-18.Similarly, where compound names include the notation [¹⁸F], for examplein reference to an “[¹⁸F]fluoro-” substituent, this indicates that thefluorine substituent in that compound is a fluorine-18 atom. Where morethan one fluorine atom is present in a radiofluorinated molecule asherein described, the molecule should be understood as containing onlyone fluorine-18 substituent unless otherwise indicated, all otherfluorine atoms in the molecule being of the ¹⁹F isotope (fluorine-19 isthe only stable naturally-occurring isotope of fluorine: isotopes offluorine other than ¹⁸F and ¹⁹F have half-lives of under a minute andtherefore have negligible abundance). The [¹⁸F] notation in such caseswill appear adjacent to the fluorine-18 substituent. Thus, for example,in [¹⁸F]fluoronicotinic acid 2,3,5,6-tetrafluorophenyl ester, thefluorine-18 atom is the fluorine substituent on the nicotinic acidmoiety, with the four fluorine atoms in the tetrafluorophenyl moietybeing fluorine-19 atoms. In the case of any ambiguity in nomenclature inpolyfluorinated compounds, the position of the ¹⁸F isotope indicated inthe corresponding structural formula should be regarded as definitive.

In a first aspect the present invention provides a radiofluorinationprocess which comprises the following steps:

-   -   (a) providing a solid stationary phase which comprises a        polymeric anion-exchange resin having bound thereto        [¹⁸F]fluoride anions; and    -   (b) contacting said solid stationary phase with a non-aqueous        solution of a precursor compound of formula (I):

-   -   optionally in the presence of an organic non-nucleophilic base,    -   whereby to produce a radiofluorinated compound of formula (II):

wherein:in formula (I), L is a positively charged leaving group, e.g. a leavinggroup selected from —NH₃ ⁺, —N(C₁₋₆ alkyl)₃ ⁺,1,4-diazabicyclo[2.2.2]octan-1-ium, and 1-(C₁₋₃ alkyl)-pyrrolidin-1-ium;andin formulae (I) and (II), R is a group of the formula:

wherein R′ is an electron-withdrawing group.

Although the use of an organic non-nucleophilic base in step (b) isoptional, the presence of such a base is preferred. Therefore, in apreferred embodiment, in step (b) the solid stationary phase iscontacted with the non-aqueous solution of the precursor compound offormula (I) in the presence of an organic non-nucleophilic base. Thus,in this embodiment, the present invention provides a radiofluorinationprocess which comprises the following steps:

-   -   (c) providing a solid stationary phase which comprises a        polymeric anion-exchange resin having bound thereto        [¹⁸F]fluoride anions; and    -   (d) contacting said solid stationary phase with a non-aqueous        solution of a precursor compound of formula (I):

-   -   optionally in the presence of an organic non-nucleophilic base,    -   whereby to produce a radiofluorinated compound of formula (II):

wherein:in formula (I), L is a positively charged leaving group, e.g. a leavinggroup selected from —NH₃ ⁺, —N(C₁₋₆ alkyl)₃ ⁺,1,4-diazabicyclo[2.2.2]octan-1-ium, and 1-(C₁₋₃ alkyl)-pyrrolidin-1-ium;andin formulae (I) and (II), R is a group of the formula:

wherein R′ is an electron-withdrawing group.

The symbol * indicates the point of attachment of group R to thepyridinyl ring.

The precursor compound of formula (I) is optionally in the form of asalt, e.g. a salt with a suitable counterion such as a chloride,bromide, phosphate, metaphosphate, perchlorate, nitrate, sulphate,tartrate, trifluoroacetate, citrate, malate, lactate, fumarate,benzoate, glycolate, gluconate, succinate, methanesulphonate,trifluoromethanesulphonate, or para-toluenesulphonate anion.

In the precursor compound of formula (I), groups L and R may be locatedin ortho-, meta- or para-positions relative to one another on thepyridinyl ring. Groups L and R may independently be located in theortho-, meta- or para-position relative to the nitrogen atom of thepyridinyl ring, i.e. these may be located at any of the available ringpositions.

The precursor compound of formula (I) may be selected from a compound offormula (Ia), (Ib), (Ic) or (Id):

(wherein L and R are as herein defined)or a salt thereof with a suitable counterion, e.g. one as hereindefined.

Precursor compounds of formulae (Ia) and (Ib) are preferred. In anembodiment the compound of formula (I) is a compound of formula (Ia) inwhich L and R are para-relative to one another.

As noted above, L is a positively charged leaving group and may, forexample, be a leaving group selected from —NH₃ ⁺, —N(C₁₋₆ alkyl)₃ ⁺,1,4-diazabicyclo[2.2.2]octan-1-ium, and 1-(C₁₋₃ alkyl)-pyrrolidin-1-ium.All leaving groups L are thus positively charged. Without wishing to bebound by theory, the present inventors believe that the positive chargeassists in the release of [¹⁸F]fluoride anions from the stationaryphase. This provides the advantage that the process of the invention canbe performed without the need to employ a phase transfer catalyst. Thepresence of a positively-charged leaving group also increases theelectron deficiency of the pyridine ring (which is already slightlyelectron deficient compared to a homoaromatic system such as a phenylring), increasing the reactivity of the precursor towards aromaticnucleophilic substitution by the released [¹⁸F]fluoride anions. Thisreactivity is still further enhanced by the presence of group R, whichcontains at least an electron-withdrawing carbonyl group as well as (incertain embodiments) a further electron-withdrawing group R′.Homoaromatic analogues of the precursor compounds of formula (I) do notdisplay the same reactivity and therefore the high reactivity, fastreaction time and good yields achieved by the process of the inventionwere not expected prior to carrying out the work described herein.

A preferred leaving group L of the type —N(C₁₋₆ alkyl)₃ ⁺ is —N(CH₃)₃ ⁺(i.e. a trimethylammonium group). A preferred leaving group L of thetype 1-(C₁₋₃ alkyl)-pyrrolidin-1-ium is 1-methylpyrrolidin-1-ium.

In an embodiment the leaving group L is —N(CH₃)₃*(trimethylammonium),1-methylpyrrolidin-1-ium, or 1,4-diazabicyclo[2.2.2]octan-1-ium. Theabbreviation “DABCO” may be employed to refer to a1,4-diazabicyclo[2.2.2]octan-1-ium leaving group.

The leaving group L is positively charged and therefore a suitablecounterion (i.e. an anion) will normally be present as part of theprecursor compound of formula (I). Any suitable counterion may beemployed with any leaving group L. Suitable counterions for any leavinggroup L herein described include those described above, i.e. chloride,bromide, phosphate, metaphosphate, perchlorate, nitrate, sulphate,tartrate, trifluoroacetate, citrate, malate, lactate, fumarate,benzoate, glycolate, gluconate, succinate, methanesulphonate,trifluoromethanesulphonate, and para-toluenesulphonate anions. In anembodiment the counterion is a chloride, bromide, perchlorate,sulphonate, nitrate, phosphate, or trifluoromethanesulphonate anion.Perchlorate or trifluoromethanesulphonate anions are preferred. Thetrifluoromethanesulphonate anion may be referred to as triflate, -OTf,OTf⁻ or simply OTf.

In certain embodiments, the group R in the precursor compounds offormula (I) is an aldehyde group, —CHO. This gives rise to thepossibility of the following precursor compounds of formula (Ie), (If),(Ig) and (Ih) and their salts:

In these compounds the leaving group L is as hereinbefore defined.

Precursor compounds of formulae (le) and (If) are preferred. In anembodiment the compound of formula (I) is a compound of formula (Ie), inwhich L and the aldehyde group are para-relative to one another.

In certain embodiments, the group R in precursor compounds of formula(I) is —COOR′, wherein R′ is an electron-withdrawing group. This givesrise to the possibility of the following precursor compounds of formula(Ii), (Ij), (Ik) and (Il) and their salts:

In these compounds the leaving group L is as hereinbefore defined.

Precursor compounds of formulae (Ii) and (Ij) are preferred. In anembodiment the compound of formula (I) is a compound of formula (Ii) inwhich the L and the ester group are para-relative to one another.

Where R is —COOR′ (thus in precursor compounds of formulae (Ii), (Ij),(Ik) and (Il)) the precursor compound may be described as an “activeester” (or “activated ester”) because the carbonyl group of the —COOR′substituent is electron-deficient and the —OR′ moiety of the —COOR′substituent is a good leaving group. The corresponding radiofluorinatedcompounds of formula (II) derived from such precursor groups may also bedescribed as “active esters” (or “activated esters”) for the samereasons. Due to the electron-deficiency of the carbonyl group and theability of the —OR′ group to act as a leaving group, “active esters” are“activated” to form amide bonds via condensation reactions with aminegroups such as amine side-chains in biomolecules (e.g. peptides).Although other compounds are also capable of amide bond formation,active esters are particularly advantageous due to their increasedreactivity and capability to react under mild aqeuous reactionconditions. Radiofluorinated active esters are therefore particularlygood radiolabelling agents for the radiolabelling of biomolecules.Methods for on-column ¹⁸F-labelling of “activated esters” to generate¹⁸F-labelled compounds suitable for use as prosthetic groups wereunknown prior to the present invention.

The electron withdrawing group R′ may be any substituent which has atendency to withdraw electron density from the carbonyl carbon atom(i.e. which is more electronegative than the carbonyl group) and whichthus increases the susceptibility of the carbonyl group to nucleophilicattack. In an embodiment the electron withdrawing group R′ is —CX₃ or—CH₂CX₃ (where each X is independently Cl or F), —CH(CX₃)₂ or —C(CX₃)₃(where each X is independently Cl or F, and each CX₃ group may be thesame or different), or a group having the structure -Ph(Z)_(n):

(where n is an integer from 1 to 5 (i.e. 1, 2, 3, 4 or 5, preferably 1or 4) and each Z is independently an electron withdrawing group, e.g.—F, —Cl, —NO₂, or —CN).

In the above structural formula for the group -Ph(Z)_(n), the symbol *indicates the point of attachment of the phenyl ring to the non-carbonyloxygen atom of the ester group, such that where R′ is a -Ph(Z) group,then group R has the structure:

(where * indicates the point of attachment of the group R to the pyridylring of the compound of formula (I)).

In an embodiment the electron withdrawing group R′ is —CF₃, —CH₂CF₃,—CH(CF₃)₂, —C(CF₃)₃, or -Ph(Z)_(n).

The precursor compound of formula (I) may be a compound of formula (Im)or (In):

wherein L, Z and n are as herein defined.

Where the electron withdrawing group R′ is a -Ph(Z)_(n) group, n may be1, 2, 3, 4 or 5 in formula (Im) or (In). Where n is 1, 2, 3, or 4,multiple regioisomers of group -Ph(Z)_(n) exist which vary in theirplacement of groups Z around the ring. All such regioisomers arecontemplated within the scope of the compounds of formula (I) as definedherein. Thus, where n=1, group R′ may have any one of the followingstructures:

Where n=2, group R′ may have any one of the following structures:

Where n=3, group R′ may have any one of the following structures:

Where n=4, group R′ may have any one of the following structures:

Where n=5, group R′ has the following structure:

In all of the above structures each group Z, independently of oneanother, may be as herein defined. As will be appreciated, inembodiments where n is 2, 3, 4 or 5, multiple further regioisomers mayalso exist where the individual groups Z are not identical to oneanother. All such regioisomers are contemplated within the scope of thecompounds of formula (I) as described herein.

Examples of electron withdrawing groups R′ having formula -Ph(Z)include, but are not limited to, -Ph(NO₂), -Ph(CN), -PhCl, -PhCl₂,-PhCl₃, -PhCl₄, -PhCl₅, -PhF, -PhF₂, -PhF₃, -PhF₄, -PhF₅, -PhClF,-PhClF₂, -PhClF₃, -PhClF₄, -PhFCl₂, -PhFCl₃, -PhFCl₄, and -PhF₂Cl₂ (allregioisomers of such groups are contemplated where such regioisomers canexist).

In preferred embodiments the precursor compound of formula (I) may be acompound of formula (Io), (Ip), (Iq) or (Ir), or a salt thereof:

In all compounds of formulas (Ia) to (Ir), L is a leaving group ashereinbefore defined and is preferably —N(CH₃)₃ ⁺ (trimethylammonium),1-methylpyrrolidin-1-ium, or 1,4-diazabicyclo[2.2.2]octan-1-ium.

Preferred precursor compounds for use in the invention are those offormula (Is) and their salts:

wherein L and R′ are as defined in Table 1:

TABLE 1 R′ L

(1) (2) (3) (4) (5) (6) (7)

(8) (9) (10) (11) (12) (13) (14)

(15) (16) (17) (18) (19) (20) (21)

This gives rise to compounds (1) to (21) and their corresponding salts.

In a particularly preferred embodiment the precursor compound of formula(I) is selected from compounds (1), (8) and (15) as defined in Table 1(and their salts). Compound (1) is especially preferred. Compound (1) isN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate.

In the process of the invention the precursor compound of formula (I)reacts with the [¹⁸F]fluoride anions eluted from the solid stationaryphase by undergoing nucleophilic aromatic substitution. This results inleaving group L being replaced by an [¹⁸F]fluoro-substituent (alsodenoted as an [¹⁸F]F substituent) to produce a radiofluorinated compoundof formula (II):

In the radiofluorinated compound of formula (II), the [¹⁸F]F substituentoccupies the same position on the pyridyl ring previously occupied bythe leaving group L. The group R remains unchanged. Therefore, allpreceding discussion of groups R, R′ and Z in the context of precursorcompounds of formula (I) applies equally to the radiofluorinatedprosthetic group of formula (II). Consequently, the radiofluorinatedcompound of formula (II) may be a compound of formula (IIa), (IIb),(IIc), (IId), (IIe), (IIf), (IIg), (IIh), (IIi), (IIj), (Ik), (II),(IIm), (IIn), (IIo), (IIp), (IIq), (IIr) or (IIs). Such compounds havestructures analogous to compounds of formulae (Ia), (Ib), (Ic), (Id),(le), (If), (Ig), (Ih), (Ii), (Ij), (Ik), (Il), (Im), (In), (Io), (Ip),(Iq), (Ir) or (Is), respectively, but with an [¹⁸F]F atom in place ofthe leaving group L.

Where the compound of formula (I) is selected from compounds (1) to (21)as defined in Table 1, the corresponding radiolabelled prosthetic groupsformed by reaction with the [¹⁸F]fluoride anion have general formula(IIs):

wherein:precursor compounds (1), (8) and (15) each react with the [¹⁸F]fluorideanion to form a radiolabelled prosthetic compound (1′); precursorcompounds (2), (9) and (16) each react with the [¹⁸F]fluoride anion toform a radiolabelled prosthetic compound (2′); precursor compounds (3),(10) and (17) each react with the [¹⁸F]fluoride anion to form aradiolabelled prosthetic compound (3′); precursor compounds (4), (11)and (18) each react with the [¹⁸F]fluoride anion to form a radiolabelledprosthetic compound (4′); precursor compounds (5), (12) and (19) eachreact with the [¹⁸F]fluoride anion to form a radiolabelled prostheticcompound (5′); precursor compounds (6), (13) and (20) each react withthe [¹⁸F]fluoride anion to form a radiolabelled prosthetic compound(6′); and precursor compounds (7), (14) and (21) each react with the[¹⁸F]fluoride anion to form a radiolabelled prosthetic compound (7′);andwherein the R′ group in general formula (IIs) in respect of each ofradiolabelled prosthetic compounds (1′) to (7′) is as defined in Table2:

TABLE 2           R′

   

   

   

 

   

Prosthetic (1′) (2′) (3′) (4′) (5′) (6′) (7′) compound

Where the compound of formula (I) is compound (1), (8) or (15) asdefined in Table 1, the resulting radiofluorinated prosthetic compoundof formula (II) is [¹⁸F]fluoronicotinic acid 2,3,5,6-tetrafluorophenylester ([¹⁸F]F-Py-TFP) which is a compound of formula (1′) as defined inTable 2. This is a particularly preferred radiofluorinated prostheticgroup.

In the process according to the invention, the precursor compound offormula (I) is provided in a non-aqueous solution. The non-aqueoussolution may be referred to as the “precursor solution”. The precursorsolution comprises the precursor compound of formula (I) and anon-aqueous solvent.

Any suitable organic solvent may be employed as the non-aqueous solvent,such as acetonitrile (“ACN”), tert-butanol, dimethylformamide (“DMF”),dimethylsulphoxide (“DMSO”), dimethylacetamide, tetrahydrofuran, dioxan,1,2-dimethoxyethane, sulpholane, N-methylpyrolidinone, or mixturesthereof. Alternatively an ionic liquid may be employed as thenon-aqueous solvent, such as an imidazolium derivative (e.g.1-ethyl-3-methylimidazolium hexafluorophosphate), a pyridiniumderivative (e.g. 1-butyl-4-methylpyridinium tetrafluoroborate), aphosphonium compound, a tetraalkylammonium compound, or mixturesthereof. The preferred non-aqueous solvent is a mixture of acetonitrileand tert-butanol in a ratio of from 1:1 to 1:9 such as 1:1 to 2:8,preferably 1:1 or 2:8.

The volume of the precursor solution to be used in the method canreadily be determined by those skilled in the art and will be dependenton factors such as the nature of the column employed. Typically, thismay have a volume of 1-5000 μL, preferably 300-1500 μL.

In the process of the invention the precursor compound of formula (I) isoptionally contacted with the stationary phase in the presence of anorganic non-nucleophilic base. The presence of an organicnon-nucleophilic base is preferred as this can be beneficial. Suitableorganic non-nucleophilic bases include N,N-diisopropylethylamine (DIPEAor Hinig's base), trimethylamine (TEA), and sym-collidine (and itsisomers). In an embodiment the precursor solution comprises 1 to 3stoichiometric equivalents (eq.) of the organic non-nucleophilic basewith respect to the precursor compound. In a preferred embodiment thebase is DIPEA or trimethylamine. Trimethylamine is particularlypreferred as this is less expensive and excess trimethylamine can beremoved more easily. In a particularly preferred embodiment of theinvention DIPEA or trimethylamine is employed in an amount of about 10to about 15 μl together with about 20 to about 40 (e.g. about 30) mg ofprecursor compound. This embodiment has been found to give particularlyadvantageous overall yields (about 60 to about 70%) of the correspondingradiolabelled prosthetic group. This embodiment has also been found togive particularly reproducible results.

In an alternative embodiment the stationary phase is pre-loaded(pre-charged) with the organic non-nucleophilic base prior tointroduction of the precursor solution. The term “stationary phase” is acommon term of the art in the field of chromatography and refers to oneof the two phases of a chromatographic system, the other phase beingreferred to as the mobile phase. The mobile phase flows through or overthe stationary phase. In the process of the present invention theprecursor solution acts as the mobile phase.

According to the invention, the solid stationary phase comprises apolymeric anion-exchange resin. The solid stationary phase may consistessentially of the polymeric anion-exchange resin or the polymericanion-exchange resin may be supported on an inert solid supportmaterial. The anion exchange resin and/or the inert solid supportmaterial (where present) may be in the form of a resin, grains, beads,membranes, sheets and/or capillaries. The anion-exchange resin is apolymeric anion-exchange resin, preferably an organic polymericanion-exchange resin and not a silica-based anion-exchange resin, sincesilica-based anion-exchange resins (particularly silica-based,hydrophilic, strong ion exchanger materials) have been found to workless efficiently with the process of the invention.

The polymeric anion-exchange resin is preferably a strong anion-exchangeresin but may also be a weak anion exchange resin or a mixture of strongand weak anion-exchange resins. The polymeric anion-exchange resin mayfor example be a resin derived from a polystyrene-divinylbenzenecopolymer or derived from a so-called “Merrifield resin” which is acopolymer of styrene and chloromethylstyrene. Preferred counter-ions forthe anion exchange resin are bicarbonate (HCO₃ ⁻), dihydrogen phosphate,monohydrogen phosphate, or any other inorganic or organic anion with apK_(a) value of 7 to 12. Where the precursor compound of group (I) is anactive ester, the counter-ion for the anion exchange resin is preferablyonly weakly basic in order to avoid base hydrolysis of the R group ofthe precursor compound. In such cases bicarbonate is particularlypreferred as the counter-ion for the anion exchange resin.

The polymeric anion-exchange resin may be provided in a chromatographiccolumn or cartridge. The term “column” or “cartridge” means any type ofconventional stationary phase apparatus which may be used inchromatography, including plastic or glass containers which contain theanion-exchange resin and allow a mobile phase to be introduced at afirst end from where it flows through or over the stationary phase undergravity and/or pressure to a second end.

Suitable anion exchange materials and chromatographic columns orcartridges bearing such anion exchange materials are commerciallyavailable and known to those skilled in the art. Examples of suitablecommercially-available polymeric anion-exchange materials andcolumns/cartridges bearing anion-exchange materials include thoseavailable under the following trade names:

From Macherey-Nagel:

-   -   CHROMABOND strong PS/DVB-anion exchanger in HCO⁻ ₃-form (PS-HCO⁻        ₃) shorty/45 mg    -   CHROMABOND strong PS/DVB-anion exchanger in other ionic forms,        shorty/45 mg

From Waters:

-   -   Oasis MAX Plus Short Cartridge, 225 mg Sorbent per Cartridge, 60        μm Particle Size    -   Oasis WAX Plus Short Cartridge, 225 mg Sorbent per Cartridge, 60        μm Particle Size

From Thermo Scientific:

-   -   HyperSep™ SAX Cartridges

From Bio-Rad:

-   -   AG resins with quaternary ammonium functional groups

From GL sciences:

-   -   MonoSpin™ SAX

From PerkinElmer:

-   -   SPE Supra-Clean® Strong Anion Exchange (SAX)

From Supelco:

-   -   Supel-Select SAX

From Phenomenex:

-   -   Strata-X-A and products with similar characteristics

From Silicycle:

-   -   SiliaPrepX™ SAX Polymeric SPE Cartridges

From Avantor:

-   -   Bakerbond Xwp 500 Polyquat-35

The columns/cartridges available from Macherey-Nagel GmbH & Co. KG,DWren, Germany, under the trade names Chromafix® and Chromabond® areparticulary preferred in the processes of the invention, in particularthe Chromafix® and Chromabond® PS-HCO₃ ⁻ and PS-CO₃ ⁻ anion exchangecolumns.

The required amount of solid phase can readily be determined by thoseskilled in the art and will be dependent on factors such as the natureof the column employed. Typically, the solid phase may be provided in anamount of 1 mg to 1000 mg, preferably 5 mg to 130 mg.

When the precursor solution contacts the stationary phase it elutes[¹⁸F]fluoride anions from the stationary phase and thus “activates” theanions for nucleophilic substitution of the leaving group L. It istherefore necessary to trap [¹⁸F]fluoride anions on the polymericanion-exchange resin before contacting the stationary phase with theprecursor solution.

The preparation and trapping of [¹⁸F] may be performed usingconventional methods. [¹⁸F]fluoride may conveniently be prepared from¹⁸O-enriched water using the (p,n) nuclear reaction as described byGuillaume et al. (Appl. Radiat. Isot. 42 (1991) 749-762). [¹⁸F]fluorideis generally isolated as an aqueous solution of H[¹⁸F]F or a salt suchas Na[¹⁸F]F, K[¹⁸F]F, Cs[¹⁸F]F, a tetraalkylammonium[¹⁸F]fluoride (e.g.tetramethylammonium[¹⁸F]fluoride) or tetraalkylphosphonium[¹⁸F]fluoride(e.g. tetramethylphosphonium[¹⁸F]fluoride).

The [¹⁸F]fluoride can be trapped on the stationary phase by passing the[¹⁸F]fluoride-containing aqueous solution (typically in an amount of 1to 5 ml) over or through the stationary phase, which traps the[¹⁸F]fluoride in the anion-exchange resin.

Prior to trapping the [¹⁸F]fluoride on the stationary phase, it may bepreferable to “condition” the resin with bicarbonate (HCO₃ ⁻)counter-ions. This may be performed according to conventional methodsknown to those skilled in the art.

In order to remove any bulk water remaining in the stationary phasefollowing the trapping of the [¹⁸F]fluoride, the stationary phase ispreferably rinsed with an organic water-miscible solvent such asacetonitrile before contacting the [¹⁸F]fluoride-bearing stationaryphase with the precursor solution. The organic solvent will alsofunction as a conditioning medium for the stationary phase. Preferably0.05 to 10 ml of organic water-miscible solvent, e.g. about 2 mL, areused for rinsing the stationary phase.

Optionally the stationary phase may be further dried with air, argon, N₂or other inert gas after rinsing with the organic water-miscible solventand before the elution step. For example, the stationary phase may bedried with 5-10 ml of air, argon, N₂ or other inert gas after rinsingwith the organic water-miscible solvent and before the elution step.

The step of eluting the trapped [¹⁸F]fluoride anions from the stationaryphase is effected by contacting the stationary phase with the precursorsolution. Preferably, this is carried out by eluting the precursorsolution through the stationary phase at a rate of <1.0 mL/minute.Preferably the elution is performed for about 1 to 3 minutes, e.g. forabout 2 to 3 minutes.

Surprisingly, the use of an electron-deficient precursor compound offormula (I) together with a polymeric anion-exchange material allowsdirect on-column reaction between the precursor and the [¹⁸F]fluoridewithout the need for a phase transfer catalyst. Thus in an embodiment ofthe invention the method is not carried out in the presence of a phasetransfer catalyst (such as those phase transfer catalysts commonly usedin PET radiochemistry for nucleophilic reactions with [¹⁸F]fluoride),for example the stationary phase is not contacted with a phase transfercatalyst during the elution step.

Following preparation of the compound of formula (II), the stationaryphase may if desired be rinsed with an organic solvent and/or an acidicaqueous solution (or a mixture of an organic solvent and an acidicaqueous solution) in order to recover any residual compound of formula(II) which may have remained on the stationary phase after the precursorsolution has passed through or over the stationary phase. Any organicsolvent as herein described is suitable for this purpose.

Previously-described attempts at on-column fluorination described in theliterature require heating of the anion-exchange resin and/or precursorsolution to elevated temperatures of 40° C. or more, such as 70-90° C.Such temperatures are not accessible on commercial radiofluorinationplatforms such as those used in hospitals or other clinical settings. Incontrast, the process of the invention can be carried out at ambienttemperature. In an embodiment the process of the invention is performedat a temperature of 35° C. or below, preferably 30° C. or below, e.g. atemperature of from 10° C. to 25° C., such as 15° C. to 25° C., 18° C.to 23° C. or 20 to 25° C.

As the process of the invention does not require the use of a phasetransfer catalyst, it is much simpler than radiofluorination processesknown in the art. In part, this is because it is not necessary to purifythe compound of formula (II) in order to remove residual phase transfercatalyst, or to perform quality control for the presence of phasetransfer catalyst in the final radiolabelled product. However, followingthe preparation of the compound of formula (II) it may nevertheless, ifdesired, be purified by standard methods, typically using solid phaseextraction, for example with an Oasis MCX™ column or a SEP-PAK™ C18 pluscolumn from which the compound of formula (II) can be eluted with goodpurity using a suitable organic solvent/water mixture. Such purificationmay be performed in order to remove intact precursor, unreacted ¹⁸F⁻ andother non-radioactive impurities deriving from the precursor.

The lack of a requirement for a phase transfer catalyst means that noseparate eluent solution containing a phase transfer agent is requiredto elute the [¹⁸F]fluoride from the stationary phase to a reactionvessel before reaction with the precursor compound can take place. Onlyone vial is needed, which can contain the precursor compound, a base(where this is present) and a non-aqueous solvent. This saves space,capacity and materials. Alternatively, the precursor can be storedseparately from the base and mixed with the base and solvent at thepoint of use, e.g. just before synthesis of the compound of formula(II); however, this still avoids the need for a separate phase transferagent solution.

The radiolabelled product forms directly on the stationary phase (e.g.on the column) during the passage of the precursor solution through thestationary phase, and so a separate reaction vessel (separate from thestationary phase, e.g. the column or cartridge) for preparation of thecompound of formula (II) is not needed.

The reaction between the precursor compound of formula (I) and the[¹⁸F]fluoride anions in the process of the invention is rapid and isessentially complete within 5 minutes (often as little as 2 to 3minutes) with no requirement for heating or cooling.

Commercially available PET automatic synthesizer platforms are normallyequipped with one reaction vessel. The present invention thereforeavoids the need to use the reaction vessel for incorporation of [¹⁸F]F⁻into the precursor. The reaction vessel will therefore be un-used andclean (e.g. not contaminated with any radioactive residue) when it isused in a subsequent conjugation step between the compound of formula(II) and the selected biomolecule.

No azeotropic drying of the fluoride is required in the process of thepresent invention, unlike conventional methods. This results in improvedyields due to less radioactive decay because of the shorter time neededto perform all process steps. The lack of azeotropic drying also avoidsabsorbance of ¹⁸F to the reaction vessel, unlike the conventionally-usedazeotropic drying regime used in ¹⁸F PET chemistry. The lack ofazeotropic drying also avoids producing volatile radioactive species.

The compounds of formula (II) can be used as prosthetic groups for thelabelling of biomolecules. The compounds of formula (II) will conjugateto a biomolecule under mild conditions, for example via an[¹⁸F]fluoroacylation or [¹⁸F]fluoroamidation reaction with an aminogroup in a peptide such as an N^(α)-terminal amino group or a lysineN^(ε)-amino group of a peptide backbone.

In an embodiment the radiofluorination process of the present inventiontherefore further comprises the step of reacting the resulting compoundof formula (II) with a compound of formula (III):

H₂N-biomolecule  (III)

to provide a radiolabelled biomolecule of formula (IV):

(wherein in formulae (III) and (IV) “biomolecule” denotes a biomoleculeor a residue or fragment thereof).

The reaction of a compound of formula (II) with a compound of formula(III) may be effected in a suitable solvent, depending on thebiomolecule(III) solubility and stability in the said solvent, forexample in an aqueous buffer in the pH range 2 to 12, suitably 7 to 11,and/or at a temperature in the range 5 to 70° C., preferably atemperature of 35° C. or below, preferably 30° C. or below, e.g. atemperature of 10° C. to 25° C., such as 15° C. to 25° C., 18° C. to 23°C. or 20 to 25° C. The choice of solvent, pH and temperature may dependon the solubility and stability of the biomolecule in the respectivesolvent under the selected conditions. The skilled person will readilybe able to select an appropriate solvent, pH and temperature using theirknowledge of the characteristics of the chosen biomolecule.

In formulae (III) and (IV) suitable biomolecules for labelling mayreadily be determined by those skilled in the art. These includepeptides, for example somatostatin analogues (such as octreotide),bombesin, vasoactive intestinal peptide, chemotactic peptide analogues,α-melanocyte stimulating hormone, urea based PSMA inhibitors,neurotensin, Arg-Gly-Asp peptide and its analogues, human pro-insulinconnecting peptide, endothelin, angiotensin andformyl-norleucyl-leucyl-phenylalanyl-norleucyl-tyrosyl-lysine, or aresidue or fragment thereof. Preferred peptides for labelling areArg-Gly-Asp peptide (“RGD peptide”) and its analogues, such as thosedescribed in WO 01/77415 and WO 03/006491, the entire contents of whichare incorporated herein by reference.

In one embodiment, suitable peptides for use in the invention comprisethe fragment:

In one embodiment, the biomolecule in formula (III) or (IV) is a peptidehaving the following structure:

wherein X⁷ is either —NH₂ or a group of formula:

wherein a is an integer of from 1 to 10, preferably wherein a is 1.

In further embodiments the biomolecule in formula (III) or (IV) is apeptide having the following structure (C):

where n may be 1, 2, 3, 4, 5, 6, 7, 8 or 9.

The radiolabelled biomolecule of formula (IV) may therefore be amolecule of the following structure:

where n is 1, 2, 3, 4, 5, 6, 7, 8 or 9.

In another embodiment (corresponding to the peptide illustrated abovewhere n=4) the biomolecule in formula (III) or (IV) is a peptide havingthe following structure:

The radiolabelled biomolecule of formula (IV) may therefore be amolecule of the following structure:

such as [¹⁸F]DCFPyL (as described in Szabo et al., Molecular Imaging andBiology, 2015, vol. 17, issue 4, pp. 565-574):

[¹⁸F]DCFPyL thus corresponds to the case where n=4, as noted above.Analogous radiolabelled biomolecules where n=1, 2, 3, 5, 6, 7, 8 or 9may also be prepared and these also form part of the invention. Thus inone embodiment the invention provides a radiolabelled biomolecule offormula (D):

wherein n=1, 2, 3, 4, 5, 6, 7, 8 or 9.

Peptides of formula (C) bind to PSMA. Without wishing to be bound bytheory, it is believed that varying the value of n allows the affinityto be varied so as to enhance or decrease the affinity of the peptidefor PSMA. The radiolabelled biomolecules derived from such peptides maytherefore also be tuned in their affinity for PSMA by appropriateselection of n. Radiolabelled biomolecules with lower values of n(particularly where n is 1, 2 or 3) are also excreted faster than thosewith higher values of n (i.e. where n is 4 or greater). This allowsradioimaging to be performed at an earlier time point and with lowerbackground.

In another embodiment, the biomolecule in formula (III) or (IV) is anaminooxy- or hydrazine-modified peptide, i.e. a peptide bearing anaminooxy or hydrazine group (e.g. as a side chain). Such modifiedpeptides are well known to those skilled in the art and may be preparedby methods such as site-specific chemical protein conjugation usinggenetically encoded aldehyde tags as described by Rabuka et al., NatureProtocols 7, 1052-1067, 2012. Aminooxy and hydrazine groups reactrapidly with aromatic aldehydes, forming oxime or hydrazone ligations,respectively. Thus aminooxy- or hydrazine-modified peptides areparticularly advantageous peptides for reaction with radiofluorinatedcompounds of formula (II) wherein R is a group

(e.g. radiofluorinated compounds of formula (IIe), (IIf), (IIg) or (IIh)as herein defined), because this allows rapid conjugation. The reactionbetween a radiofluorinated compound of formula (II) wherein R is a group

is preferably performed at a pH of from about 2 to about 5, (e.g. pH2-5, pH 2-4, pH 2-3, pH 3-5, or pH 4-5, such as pH 2, pH 3, pH 4 or pH5) as this minimises reaction with free amine groups, which areprotonated in this pH range, thereby allowing site-specificradiolabelling of the aminooxy and/or hydrazine groups of the modifiedpeptide.

Aminooxy-modified peptides may have the following structure:

(wherein “peptide” denotes a peptide or a peptide residue or fragment).

An example of an aminooxy-modified peptide isAminooxyacetyl-Leu-Glu-Phe-NH₂ as reported in, for example, Poethko etal., The Journal of Nuclear Medicine, Vol. 45, no. 5, May 2004.

An example of a hydrazine-modified peptide is6-hydrazinopyridyl-functionalized human serum albumin (HYNIC-HSA) asreported in, for example, Dirksen et al., Bioconjug. Chem., 2008,19(12), 2543-2548.

As will be appreciated by the skilled person, the methods of theinvention may also be used for [¹⁸F]fluorination of other biomolecules,such as proteins, hormones, oligonucleotides, and antibody fragments, aswell as small drug-like molecules to provide a variety of PET tracers.

Compounds of formula (III) may be prepared by standard methods ofpeptide synthesis, for example, solid-phase peptide synthesis (see e.g.Atherton, E. and Sheppard, R. C.; “Solid Phase Synthesis”; IRL Press:Oxford, 1989). Incorporation of the primary amine group in a compound offormula (III) may be achieved by reaction of the N or C-terminus of thepeptide or with some other functional group contained within the peptidesequence, modification of which does not affect the bindingcharacteristics of the vector. The primary amine group is preferablyintroduced by formation of a stable amide bond formed by reaction of apeptide amine function with an activated acid and introduced eitherduring or following the peptide synthesis. When the precursor is an acidthen the primary amine can be introduced using in situ activating agentssuch as 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluroniumhexafluorophosphate (HBTU) orN-[(dimethylamino)-1H-1,2,3-triazolo[4,5-b]pyridin-1-ylmethylene]-N-methylmethanaminiumhexafluorophosphate N-oxide (HATU).

In another embodiment the radiofluorination process of the presentinvention further comprises the step of reacting the compound of formula(II) with a compound of formula (A):

H₂N—R″  (A)

wherein R″ denotes a C₁₋₃ alkyl group optionally substituted by a group—N(R′″)₂ and wherein each R′″ group is independently selected from C₁₋₃alkyl and H.

Preferably in such embodiments of the invention the compound of formula(II) is a compound in which the group R is —COOR′ as described herein,such that the compound of formula (II) is a compound of formula (IIi),(IIj), (Ilk) or (Il) as described herein.

Reaction of a compound of formula (II) with a compound of formula (A)therefore provides a compound of formula (B):

A preferred group —N(R′″)₂ is —N(CH₂CH₃)₂. A particularly preferredcompound of formula (A) is N,N-diethyleneethylenediamine:H₂NCH₂CH₂N(CH₂CH₃)₂. Thus, preferred compounds of formula (B) are thoseof formula (BB):

A particularly preferred compound of formula (BB) is [¹⁸F]MEL050:

[¹⁸F]MEL050 may for example be obtained by reacting [¹⁸F]F-Py-TFP withN,N-diethyleneethylenediamine. This may be carried out after synthesisof [¹⁸F]F-Py-TFP in accordance with the methods of the invention.[¹⁸F]MEL050 is particularly useful as a melanoma tracer.

Certain compounds of formula (B) and formula (BB) are themselves noveland therefore in a further embodiment the present invention providescompounds of formula (B), preferably of formula (BB), as describedherein, with the proviso that the compound is not [¹⁸F]MEL050. Precursorcompounds of formula (I) and salts thereof may be prepared fromcommercially available starting materials. Where the group R is an ester(—COOR′) the precursor compound may for example be prepared by reactinga carboxylic acid of formula (V) with an alcohol of formula R′—OH (whereR′ has the meaning as herein described) under standard esterificationconditions, for example in the presence of N,N′-Dicyclohexylcarbodiimideor an acid catalyst such as sulphuric acid:

followed by nucleophilic aromatic substitution of the Cl substituentusing a precursor of L such as trimethylamine (where L is —NMe₃ ⁺),4-diazabicyclo[2.2.2]octane (where L is DABCO) or N-methyl pyrrolidine(where Lis 1-methyl-pyrrolidin-1-ium). The nucleophilic aromaticsubstitution may typically be performed using THF as the solvent.

The preparation ofN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate starting from 6-chloronicotinic acid isdescribed in Olberg et al. (Journal of Medicinal Chemistry, 53,1732-1740 (2010)). Other compounds of general formula (I) where R is—COOR′ may be prepared analogously.

Where the group R is an aldehyde (—CHO) the precursor compound may forexample be prepared by reacting an aldehyde of formula (VI) with aprecursor of L such as trimethylamine (where L is —NMe₃ ⁺) or N-methylpyrrolidine (where L is 1-methyl-pyrrolidin-1-ium) in a nucleophilicaromatic substitution reaction:

The process according to the invention relates to synthesis methods forlabelling compounds with the positron emitter fluorine-18 which may beused in positron emission tomography (PET) imaging. Therefore in afurther embodiment the present invention provides a positron emissiontomography imaging method comprising the following steps:

-   -   (a) preparing a compound of formula (II) by the        radiofluorination process as herein described;    -   (b) reacting the compound of formula (II) with a compound of        formula (III) as herein described whereby to provide a        radiolabelled biomolecule of formula (IV) as herein described;    -   (c) administering said radiolabelled biomolecule of formula (IV)        to a human or animal (e.g. mammalian) subject; and    -   (d) acquiring a PET image of said subject.

In a further embodiment the present invention provides a positronemission tomography imaging method comprising acquiring a PET image of ahuman or animal (e.g. mammalian) subject to whom a radiolabelledbiomolecule of formula (IV) as herein described has been administered.

The administration of the biomolecule of formula (IV) is preferablyperformed by intravenous administration. The PET image may be acquiredusing any conventional PET imaging apparatus.

PET imaging is a powerful diagnostic tool in many branches of medicineand can be used to assist in the diagnosis of diseases and conditionsincluding, but not limited to, cancer (e.g. in Hodgkin's lymphoma,prostate cancer, breast cancer, clear cell renal cell carcinoma,non-Hodgkin lymphoma, lung cancer, adrenocortical tumours, andpheochromocytoma); neurological diseases such as Alzheimer's disease;neuropsychiatric conditions such as schizophrenia or mood disorders;cardiological diseases such as hibernating myocardium oratherosclerosis; or infectious diseases. Thus in a further embodimentthe present invention provides a method of diagnosis comprisingperforming a PET imaging method as herein described and making adiagnosis on the basis of the acquired PET image. The diagnosis maydesirably be a diagnosis of any of the aforementioned diseases orconditions.

PET imaging (including the PET imaging methods of the invention) canalso be employed for non-diagnostic purposes such as the study ofpharmacokinetics, neuropsychology, and musculoskeletal imaging.

The PET image acquired in the imaging methods and/or method of diagnosisaccording to the invention can, for example, be an image of the wholebody, the brain, bone, the lungs, the heart, the digestive system, themusculoskeletal system, the vascular system, the liver, the kidneys, orthe lymphatic system, or any combination or portion thereof.

Certain precursor compounds of formula (I) and their correspondingradiofluorinated derivatives (prosthetic groups) are themselves new andform further aspects of the invention.

In another aspect the present invention thus provides a compound offormula (I′):

(wherein L is as hereinbefore defined), optionally in the form of a saltwith a suitable counterion as hereinbefore described, such as achloride, bromide, phosphate, metaphosphate, perchlorate, nitrate,sulphate, tartrate, trifluoroacetate, citrate, malate, lactate,fumarate, benzoate, glycolate, gluconate, succinate, methanesulphonate,trifluoromethanesulphonate, or para-toluenesulphonate anion.

Compounds of formulae (le), (If), (Ig) and (Ih) are all compounds offormula (I′). Such compounds and their salts with a suitable counterion(such as those herein described) form a further aspect of the invention.

In an embodiment the compound of formula (I′) is a5-formyl-N,N,N-trimethylpyridin-2-aminium salt, e.g. thetrifluoromethanesulfonate salt.

Other novel compounds of formula (I) include those of formula (I″):

(where R′ is as hereinbefore defined and L′ is1,4-diazabicyclo[2.2.2]octan-1-ium or 1-(C₁₋₃ alkyl)-pyrrolidin-1-ium,e.g. 1-methyl-pyrrolidin-1-ium), optionally in the form of a salt with asuitable counterion as hereinbefore described such as a chloride,bromide, phosphate, metaphosphate, perchlorate, nitrate, sulphate,tartrate, trifluoroacetate, citrate, malate, lactate, fumarate,benzoate, glycolate, gluconate, succinate, methanesulphonate,trifluoromethanesulphonate, or para-toluenesulphonate anion.

In an embodiment the compound of formula (I″) is a compound of formula(Im″)

(wherein L′, Z and n have the meanings described above), optionally inthe form of a salt with a suitable counterion as hereinbefore describedsuch as a chloride, bromide, phosphate, metaphosphate, perchlorate,nitrate, sulphate, tartrate, trifluoroacetate, citrate, malate, lactate,fumarate, benzoate, glycolate, gluconate, succinate, methanesulphonate,trifluoromethanesulphonate, or para-toluenesulphonate anion.

In another embodiment the compound of formula (I″) is a compound offormula (In″):

(wherein L′, Z and n have the meanings described above), optionally inthe form of a salt with a suitable counterion as hereinbefore describedsuch as a chloride, bromide, phosphate, metaphosphate, perchlorate,nitrate, sulphate, tartrate, trifluoroacetate, citrate, malate, lactate,fumarate, benzoate, glycolate, gluconate, succinate, methanesulphonate,trifluoromethanesulphonate, or para-toluenesulphonate anion.

In an embodiment the compound of formula (I″) is a1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumsalt, e.g. the trifluoromethanesulfonate salt.

The [¹⁸F]fluoro-substituted compounds of formula (II) which are obtainedby reaction of the new compounds of formula (I′) with [¹⁸F]fluorideanions are themselves also new and form part of the invention. Thus inanother aspect the invention provides a radiofluorinated compound offormula (II′):

In an embodiment the compound of formula (II′) is6-[¹⁸F]fluoropyridine-3-carboxaldehyde.

The radiofluorinated analogs of compounds of formula (Im″) and (In″)also form part of the invention.

Methods for the preparation of any of the novel compounds hereindescribed, including methods for radiofluorination of any of theprecursor compounds, also form part of the invention. Methods forpreparing such compounds and for performing radiofluorination are asdescribed above.

Methods for preparing a radiofluorinated biomolecule comprising the stepof reacting any of the novel radiofluorinated compounds (prostheticgroups) with a compound of formula (III) as defined herein form afurther aspect of the invention. The resulting labelled biomoleculesalso form part of the invention as do their use as radiopharmaceuticals,for example in PET imaging methods.

The invention will now be illustrated by means of the followingnon-limiting Examples and the attached Figures in which:

FIG. 1 shows a schematic for the preparation of [¹⁸F]F-Py-TFP inaccordance with the invention as described in non-limiting Example 6.

FIG. 2 shows a non-limiting schematic of a reaction process forproducing [¹⁸F]F-Py-TFP in accordance with the invention, where:

denotes a solid phase support with anion exchange properties.

FIG. 3 shows a non-limiting schematic of a reaction process forproducing an [¹⁸F]fluorinated compound starting from a precursor havingan aldehyde substituent in accordance with the invention.

EXAMPLE 1 Experimental:

Chemicals and solvents of reagent grade obtained commercially were of apurity of 95% and were used without further purification. Water(ultra-pure, ion-free) was obtained from a Millipore Ultra-pure watersystem. HPLC solvents were obtained from Merck KGaA (VWR). Synthesis of6-fluoronicotinic acid 2,3,5,6-tetrafluorophenyl ester (F-Py-TFP) andN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate was performed as previously reported by Olbeget al. (J. Med. Chem, 53: 1732-1740).

Radiochemistry: Radiochemical synthesis was performed manually behindlead shield using aqueous [¹⁸F]fluoride obtained from a cyclotron (GEPETtrace 6) using ¹⁸O(p,n)¹⁸F nuclear reaction with a 16.5 MeV protonirradiation. Typically experiments were conducted with 30 to 62 MBq of¹⁸F starting radioactivity.

Analytical HPLC was performed on an Agilent system (1200 series) with UVdetection at 214 and 254 nm in series with a γ-detector (Raytest GABIStar 1207 radiometric detector, Straubenhardt, Germany) equipped withC-18 reversed-phase column (ACE analytical 4.6×50, 5μ) using a gradientof 10-95% solvent B in water/0.1% TFA over 10 min with a flow rate of1.0 mL/min. EZchrome software was used to record and analyze both UV andradiometric data. Radio-TLC was recorded using a Gina Star TLC andanalyzed using the Raytest miniGita software (Straubenhardt, Germany).Acetonitrile was used as the mobile phase. Radioactivity was assayedusing a calibrated Capintec CRC-15R dose calibrator (Ramsey, N.J., USA)

Experiment 1

31.3 MBq of [¹⁸F]fluoride obtained from an aqueous solution was trappedon Chromafix/Chromabond PS-CO₃ ⁻ anion exchange column (type shorty,MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany). The column wasimmediately rinsed with 2 mL of dry acetonitrile and purged with air (6mL with syringe) after which it was incubated at room temperature with a0.5 ml mixture containing 22.94 mg ofN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate (1 eq.) precursor, 8 μL DIEPA (1 eq.) in 1:1acetonitrile/t-BuOH for 2 min and 30 seconds before the solution waspushed completely through the column manually with a syringe filled withair into an empty 3 ml glass vessel (receiving vial) and immediatelyanalyzed by radio-TLC and HPLC. The radioactivity in the receiving vialwas 20.5 MBq measured in a dose calibrator 9 min after trapping of[¹⁸F]fluoride (31.3 MBq) on the column. Radio-HPLC showed a majorradioactive peak at 254 nm co-eluting with the reference standard,confirming identity, and radio-TLC showed 92.5% radiochemical yield of[¹⁸F]F-Py-TFP.

Experiment 2

65.1 MBq of [¹⁸F]fluoride obtained from an aqueous solution was trappedon Chromafix/Chromabond PS-CO₃ ⁻ anion exchange column (type shorty,MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany). The column wasimmediately rinsed with 2 mL of dry acetonitrile and purged with air (6mL with syringe) after which it was incubated at room temperature with a0.5 ml mixture containing 30 mg ofN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate (1 eq.) precursor, 14 μL triethylamine (1.5eq.) in 1:1 acetonitrile/t-BuOH for 2 min and 30 seconds before thesolution was pushed completely through the column manually with asyringe filled with air into an empty 3 ml glass vessel (receiving vial)and analyzed by radio-TLC and HPLC. The radioactivity in the receivingvial was 40.5 MBq measured in a dose calibrator 10 min after trapping of[¹⁸F]fluoride (65.1 MBq) on the column. Radio-HPLC showed a majorradioactive peak co-eluting with the reference standard (Rt=7.9 min),confirming identity, and radio-TLC showed 95% radiochemical yield of[¹⁸F]F-Py-TFP.

EXAMPLE 2

Experimental:

Chemicals and solvents of reagent grade were obtained as detailed inTable 3 and were used without further purification. Water (ultra-pure,ion-free) was obtained from a Millipore Ultra-pure water system. HPLCsolvents were obtained from Merck KGaA (VWR).

Radiochemistry, analytical HPLC, radio-TLC and radioactivity assays wereperformed as described in the Experimental section of Example 1.

TABLE 3 Chemical/ d Solvent Supplier Cat. No Grade Lot/Batch MW (g/ml) RS THF Alfa A12686 97% 10181607 NA 36/37/ 26-36 Aesar 38 DichloromethaneFluka 66749 Puriss 1208726 40 23-24/ 25-36/ 37 1M Acros 388371000A0338939 NA trimethylamine in THF Trimethylsilyl Aldrich 225649 222.261.228 trifluoromethane sulfonate (TMSOTf) 6-chloropyridine- Aldrich596175 96% MKBF5178 141.56 3-carboxaldehyde

Synthesis of 5-formyl-N,N,N-trimethylpyridin-2-aminiumTrifluoromethanesulfonate

To a solution of 6-chloropyridine-3-carboxaldehyde (700 mg, 4.9 mmol) inTHF (5 ml) was added 1 M trimethylamine solution in THF (10.0 mL). Thereaction was stirred overnight at room temperature during which a whiteprecipitate formed.

The precipitate (ammonium chloride salt) was filtered off and washedwell with dichloromethane and diethyl ether and dried (Yield: 460 mg,2.3 mmol). Under an N₂ atmosphere the ammonium salt was suspended indichloromethane (DCM) (50 ml) cooled on an ice bath and TMSOTf (0.5 mL,2.5 mmol) was added under vigorous stirring. The reaction was allowed toproceed for 30 min on ice after which it was allowed to reach roomtemperature. When the solid was completely solubilized in the DCM, theorganic phase was removed under vacuum. The solid was taken up inacetonitrile (ACN) and filtered and the filtrate was again taken andtreated under vacuum to dryness. The solid was precipitated in diethylether and filtered off. The solid was dried under high vacuum for twohours. Yield: 0.656 g, 2.1 mmol (43%) (Faint yellowish solid).

NMR analysis confirmed the successful synthesis with the followingpeaks:

¹H NMR (400 MHz, CD₃CN): δ 1.19 (s, 1H), δ 9.07 (d, J=1.8 Hz, 1H), δ8.56 (dd, J₁=2.2 Hz, J₂=8.6 Hz, 1H), 8.04 (d, J=8.6 Hz, 1H), 3.58 (s,9H).

¹³C NMR (101 MHz, CD₃CN): δ 191.40, 151.80, 142.68, 134.65, 117.00,56.51.

¹⁹F NMR (376 MHz, CDCl₃): δ-74.03.

Radiolabeling on Solid Phase of5-formyl-N,N,N-trimethylpyridin-2-aminium Trifluoromethanesulfonate with[¹⁸F]fluoride

47.2 MBq of [¹⁸F]fluoride obtained from an aqueous solution was trappedon a Chromafix/Chromabond PS-CO₃ ⁻ anion exchange column (type shorty,MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany). The column wasimmediately rinsed with 2 mL of dry acetonitrile and purged with air (6mL with syringe) after which it was incubated at room temperature with a0.5 ml mixture containing 20.3 mg of5-formyl-N,N,N-trimethylpyridin-2-aminium trifluoromethanesulfonate in1:1 acetonitrile/t-BuOH for 5 minutes before the solution was pushedcompletely through the column manually with a syringe filled with airinto an empty 3 ml glass vessel (receiving vial) and immediatelyanalyzed by HPLC. The radioactivity in the receiving vial was 15.6 MBqmeasured in a dose calibrator 10 min after trapping of [¹⁸F]fluoride(47.2 MBq) on the column. Radio-HPLC (ACE 3 C₁₈-50*4.6 mm, 5-50%acetonitrile over 10 min in water/0.05% TFA, 1 ml/min) of eluate showeda major radioactive peak eluting at 3.2 min vs. 1.4 min for precursor. Asample from the receiving vial spiked with reference standard,6-fluoropyridine-3-carboxaldehyd (t_(R)=3.16 min), confirmed theidentity of the radioactive product using the same above stated HPLCconditions.

Purification of the synthesized 6-[¹⁸F]fluoropyridine-3-carboxaldehyde

The SPE column used was Sep-Pak Oasis™ MCX plus (Waters) (strong cationexchange/with reversed phase properties for trapping unreactedprecursor). Conditioning of the SPE column was performed by using 5 mLEtOH then 5 mL MQ water followed by an air purge. The crude reactionproduct was diluted in water (6 mL) and loaded onto MCX cartridgefollowed by a 5 mL air purge. The column bound6-[¹⁸F]Fluoropyridine-3-carboxaldehyde was eluted off with 1 mL ACN.

8.72 MBq of pure 6-[¹⁸F]Fluoropyridine-3-carboxaldehyde were obtainedfrom the Oasis MCX cartridge in 1 mL MeCN (19% radiochemical yield,non-decay-corrected, 60 min after start of synthesis). HPLC confirmedremoval of the major bulk of the non-reacted precursor from the reactionmixture.

HPLC and Radio-TLC assays performed in accordance with Example 1confirmed the purified radiolabelled product,6-[¹⁸F]Fluoropyridine-3-carboxaldehyde in a radiochemical purity >95%.

EXAMPLE 3 Synthesis of1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumtrifluoromethanesulfonate

Synthesis of1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumtrifluoromethanesulfonate was performed in line with the synthesis ofN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate as previously reported by Olberg et al. (J.Med. Chem, 53: 1732-1740), but employing N-methyl pyrrolidine in placeof trimethylamine:

To a stirred solution of 2,3,5,6-tetrafluorophenyl 6-chloronicotinate(500 mg, 2.54 mmol) in 5 ml dry THF was added 1 mL ofN-methylpyrrolidine. A white precipitate started to form after 10minutes and reaction was allowed to proceed overnight. The precipitatewas collected and washed with cold Et20. The solid residue was suspendedin CH₂Cl₂, and TMSOTf (1 mL, 5.29 mmol) was added over 3 min. Themixture was concentrated, and the residue was recrystallized from Et20to afford1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumtrifluoromethanesulfonate as a white solid (0.70 g, 55%)

The identity of the synthesised product was confirmed by NMR with thefollowing peaks:

¹H NMR (400 MHz, Acetonitrile-d₃) δ 9.32 (dd, J=2.3, 0.8 Hz, 1H), δ 8.83(dd, J=8.7, 2.3 Hz, 1H), δ 8.01 (dd, J=8.7, 0.8 Hz, 1H), δ 7.43 (m, 1H),δ 4.23 (m, 2H), δ 4.01 (m, 2H), δ 3.46 (s, 3H), 2.34 (m, 2H), 2.24 (m,2H).

¹⁹F NMR (376 MHz, Acetonitrile-d₃) δ-79.36 (s), δ-140.36 (m), δ-154.41(m).

Radiolabeling on solid phase of1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumtrifluoromethanesulfonate

49.5 MBq of [¹⁸F]fluoride obtained from an aqueous solution was trappedon a Chromafix/Chromabond PS-CO₃ ⁻ anion exchange column (type shorty,MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany). The column wasimmediately rinsed with 2 mL of dry acetonitrile and purged with air (6mL with syringe) after which it was incubated at room temperature with a0.5 ml mixture containing 30.24 mg1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumtrifluoromethanesulfonate and 10 μL triethylamine in 1:1acetonitrile/t-BuOH for 2.5 minutes before the solution was pushedcompletely through the column manually with a syringe filled with airinto an empty 3 ml glass vessel (receiving vial) and immediatelyanalyzed by HPLC. The radioactivity in the receiving vial was 23.0 MBqmeasured in a dose calibrator 14 min after trapping of [¹⁸F]fluoride(49.5 MBq) on the column. Radio-HPLC (ACE 3 C18-50*4.6 mm, 10-90%acetonitrile over 10 min in water/0.05% TFA, 1 ml/min) of the eluateshowed a major radioactive peak co-eluting with F-Py-TFP referencestandard at 7.890 min.

EXAMPLE 4

Solid-phase labeling experiments were carried out using Chromafix(Chromabond PS-HCO₃) as the stationary phase. Details are shown in Table4, where:

Column A is the experiment number

Column B is the precursor amount in mg

Column C identifies the solvent and its overall volume in mL; thus, forexample, “1:1

t-BuOH/MeCN/0.5” refers to a 1:1 mixture of t-BuOH and MeCN with anoverall volume of 0.5 mL

Column D identifies the base

Column E identifies the amount of Chromafix PS-HCO₃ resin employed in mg

Column F identifies the initial radioactivity trapped on the column MBq

Column G identifies the experiment start time (hh:mm)

Column H identifies the radioactivity in MBq in the vial used to receivethe eluted radiolabelled product

Column I identifies the experiment end time (hh:mm)

Column J identifies the reaction yield (%) identified by radio-TLC

Column K identifies the elution efficiency (%)

Column L identifies the total yield (not decay-corrected) in %

TABLE 4 A B C D E F** G H I J** K*** L**** 1 21 MeCN/1 NA 45 62.8 14:0622.4 14:25 63.3 35.7 22.6 2 NA MeCN/1 + 1 NA NA NA NA 23.1 NA 79.7 NA NA3 41 MeCN/0.5 NA 45 64.0 15:00 25.7 15:15 88.6 40.1 35.5 4 NA MeCN/0.5NA 45 20.7 15:19 34.4 15:20 94.8 NA NA 5 45.7 MeCN/1 NA 45 35.2 13:2414.3 13:40 75.7 40.1 30.4 6 NA NA NA 45 NA NA NA NA 81.0 NA NA 7 24.81:1 NA 45 37.5 14:27 32.9 14:26 0 91.4 0 MeOH/MeCN/ 0.5 8 21 1:1 NA 4536.0 15.31 2.19 15:38 95.3 60.8 57.9 t-BuOH/MeCN/ 0.5 9 NA NA NA NA NANA NA NA 98.4 60.8 NA 10 23 1:1 NH₄OTf 45 47.9 11:18 12.5 11:27 17.026.1 4.4 t-BuOH/MeCN/ 0.5 11 22 8:2 NA 45 25.9 11:43 11.4 11:51 89.644.0 39.4 t-BuOH/MeCN/ 0.5 12 40 1:1 NA 25 41.7 13:55 20.3 14:05 87.748.7 42.7 t-BuOH/MeCN/1 13 20 1:1 NA 45 29.5 14:15 8.7 14:22 90.2 29.526.6 t-BuOH/MeCN/ 0.5 14 20 1:1 NA 45 40.6 15:38 18.8 15:47 81.8 46.337.9 t-BuOH/MeCN/ 0.5 15 40 1:1 NA  45# 27.5 11:50 9.6 12:00 76.8 34.926.8 t-BuOH/MeCN/ 0.5 16 40 1:1 NA 10 27.2 12:26 12.1 12:33 NA 44.5 NAt-BuOH/MeCN/ 0.5 17 22 1:1 NA ## 33.6 13:27 0.3 13:33 NA 0.9 NAt-BuOH/MeCN/ 0.5 18 23 1:1 DIPEA 45 30.9 14:19 20.5 14:26 92.5 66.3 61.3t-BuOH/MeCN/ 8 μL 0.5 19 23 1:1 DIPEA 8 μL + 45 22.5 15:12 15.2 15:1978.7 67.6 53.2 t-BuOH/MeCN/ TBAOTf 0.5 20 15 1:1 NA 45 NA NA NA NA NA NANA t-BuOH/MeCN/ 0.5 21 20 1:1 DIPEA 5 μL 45 23.2 14:17 8.7 14:24 NA 37.5NA t-BuOH/MeCN/ 0.5 22 24 1:1 DIPEA 45 16.2 14:53 10.0 14:59 NA 61.7 NAt-BuOH/MeCN/ 10 μL 0.5 23 23 1:1 DIPEA 45 43.4 15:19 29.3 15:26 70.767.5 47.7 t-BuOH/MeCN/ 12 μL 0.5 24 20 1:1 TEA 45 44.6 15:32 24.6 15:40NA 55.2 NA t-BuOH/MeCN/ 6 μL 0.5 25 30 1:1 TEA 45 63.2 14:44 40.5 14:5095.1 64.1 61.0 t-BuOH/MeCN/ 14 μL 0.5 26 22 1:1 DIPEA 45 28.7 11:57 15.712:05 66.0 54.7 37.7 t-BuOH/MeCN/ 10 μL 0.5 27 22 1:1 TEA 45 24.3 12:1713.7 12:22 42.3 56.4 23.9 t-BuOH/MeCN/ 10 μL 0.5 28 45 1:1 TEA 45 39.613:36 20.7 13:44 98.24***** 52.3 NA t-BuOH/MeCN 20 μL 0.5 29 23 1:1 TEA45 46.2 15:03 27.4 15:13 36.7 59.3 21.7 t-BuOH/MeCN/1 20 μL NA = notapplicable *After rinsing column with MeCN **Mobile phase 100% MeCN(some hydrolysis of ester may occur during drying of TLC strip (silica),and actual yield may be under estimated depending on hold-up time ofsample on strip) ***Elution efficiency is not corrected for decay andtherefore slightly underestimated depending on time between measurements****RCY by radio-TLC multiplied by elution efficiency *****Purity afterC18 Sep-Pak purification. 16.2 MBq eluted in 1 ml diethyl ether (13:55)from column showing 17. MBq at 13:51, 0.81 MBq remaining on column at13:56 #conditioned with KOTf 0.2M ## Waters QMA resin 10 mg

Comments to Entries in Table 4:

-   -   1. Eluted over 10 minutes (500+200+300). 2 mL MeCN followed by        110 sec He 1000 mL/min    -   2. Column from 1 re-eluted with additional 1 mL neat MeCN to        reaction mixture of entry 1 and heated at 40° C. for 10 min    -   3. Column treated with He-gas for 120 sec after wash with MeCN.        10 min incubation of precursor mixture on column    -   4. Same column from 3 re-treated with 0.5 of precursor mix (41        mg/mL) and 10 min incubation, eluted to mixture of 3—elution mix        heated to 40° C. for 10 min. Some radioactivity lost to        sampling.    -   5. Elution done in steps over 5 min—pulling Rx back and forth        over column.    -   6. Same as 5 heated to 50° C. for 10 min    -   7. 2 min soak—no Rx.    -   8. 2 min and 30 sec soak. (2 ml MeCN rinse before Rx)—remaining        12.7 MBq on column at 15:37    -   9. Same 9 reaction mixture heated to 40° C. for 5 min    -   10. 2 min and 30 sec soak. 60 μL of 1M NH₄OTf added to elution        mixture (Triflate salt acidic—impurities can be adjusted with        base)    -   11. 2 min and 30 sec soak    -   12. Elution mix pushed in steps over 5 min. Pressure was also        applied to column when eluting    -   13. Elution mix pushed in steps over 5 min    -   14. 250 μL of precursor eluent pushed through column and column        heated in Scansys reactor at 60° C. for 5 min before eluting        with last 250 μL of precursor eluent    -   15. i) Cartridge washed with 10 mL MQ water        -   ii) Conditioning with KOTf_((aq)) (0.2 M) 10 mL        -   ii) Wash with water—10 mL        -   Rx with precursor mixture in two steps—where elution mix is            reintroduced over column a 2^(nd) time (only final result            reported). 1 mL of 0.9% NaCl releases remaining activity on            column    -   16. 0.5 MBq bleed through column (12:32). Dropwise elution over        2 min. No effect of re-elution with reaction mixture    -   17. Rx—with silica based anion-exchange resin. 2 min and 30 sec        soak. Practically no activity eluted off column    -   18. Non-nucleophilic base added to elution mixture. 2 min and 30        sec soak. No apparent precipitation after 30 min    -   19. TBA-OTf in t-BuOH/MeCN 1:1 20 μL added to precursor mixture.        2 min and 30 sec soak    -   20. Added 10 μL of 0.9% NaCl to elution mixture. Only 10%        activity off column    -   21. Column rinse with only 1 mL acetonitrile. 2 min and 30 sec        soak    -   22. 2 min and 30 sec soak. Column rinse with only 2 mL        acetonitrile    -   23. 2 min and 30 sec soak. Column rinse with only 2 mL        acetonitrile    -   24. New batch of Chromabond PS—HCO₃ columns. 2 min and 30 sec        soak. Column rinse with only 2 mL acetonitrile    -   25. Chromabond not conditioned with water before use, incubated        with MeCN for 30 min before use    -   26. No conditioning of column, observed no bleed through of        fluoride. Soak with MeCN (5 min) after trapping fluoride. Column        rinse with only 2 mL acetonitrile    -   27. MeCN conditioning of column (5 min), no bleed through of        fluoride. Column rinse with only 2 mL acetonitrile (as normally        done). 2 min and 30 sec soak    -   28. 2 min and 30 sec soak. Crude loaded onto C18 Sep-Pak after        diluting with 5 ml 2% acetic acid solution, rinsed with water (5        mL) and eluted off with diethyl ether (1 mL)    -   29. Column conditioned with water and then 5 min soak with MeCN        before use

EXAMPLE 5

Solid-phase labeling experiments were carried out using variousdifferent resins as the stationary phase. Chromafix (ChromabondPS-HCO₃), as employed in Example 4, was used as a control (entry 3 inthe table). Details are shown in Table 5, where Columns A-D and F-Ldenote the same meanings as in Example 4. Column E identifies the typeand amount of anion exchange resin employed in mg, with bicarbonate asthe counterion. Table 5:

A B C D E F* G H I J** K*** L**** 1 30 1:1 TEA Bakerbond 22.7 12:22 5.612:32 NA# 24.7 NA t-BuOH/ (14 μL) XWP 500 MeCN/0.5 PolyQuat- 35/41 mg 230 1:1 TEA Waters 27.4 12:46 15 12:54 70.0 56.6 39.6 t-BuOH/ (14 μL)Oasis MAX MeCN/0.5 resin/43 mg 3 30.4 1:1 t- TEA Chromabond- 28.3 13:1517.7 15:23 95.8 62.5 59.9 BuOH/MeCN/ (14 μL) PS HCO₃₋ 0.5 45 mg 4 22 1:1t- NA Waters 32.3 13:24 0.3 13:33 NA 0.93 NA BuOH/MeCN/ QMA resin/ 0.510 mg #= poor elution. *After rinsing column with MeCN **Mobile phase100% MeCN (some hydrolysis of ester may occur during drying of TLC strip(silica), and actual yield may be under estimated depending on hold-uptime of sample on strip) ***Elution efficiency is not corrected fordecay and therefore slightly underestimated depending on time betweenmeasurements ****RCY by radio-TLC multiplied by elution efficiency

Comments to Entries in Table 5:

-   -   30. 2 min and 30 sec soak. Column rinse with only 2 mL        acetonitrile. HPLC confirms product in high radiochemical        purity. (Polymer based)    -   31. 2 min and 30 sec soak. Column rinse with only 2 mL        acetonitrile. HPLC and TLC confirms product in high        radiochemical purity. (Polymer based)    -   32.2 min and 30 sec soak. Column rinse with only 2 mL        acetonitrile (as normally done). HPLC and TLC confirms product        in high radiochemical purity. (Polymer based)    -   33. Practically no elution using Waters QMA resin (silica based)

EXAMPLE 6

FIG. 1 shows a schematic example of the synthesis of [¹⁸F]F-Py-TFP usingthe process of the invention. A Chromafix PS-HCO₃ ⁻ cartridge (a strongPS/DVB anion exchanger in HCO₃ ⁻ form) is loaded with 1 to 5 mL ofaqueous [¹⁸F]F⁻. The cartridge is dried by rinsing with 2 mL dryacetonitrile and then 5-10 ml of air.

20 mg of precursor(N,N,N-trimethyl-5[(2,3,5,6-tetrafluorophenoxy)carbonyl]pyridin-2-aminiumtrifluoromethanesulfonate) in 8 μl N,N-diisopropylethylamine are elutedthrough the column for 2 to 3 minutes at room temperature. Following theelution of the precursor the cartridge is rinsed with 250 μl dryacetonitrile and 250 μl dry t-BuOH. [¹⁸F]F-Py-TFP is recovered in goodyield.

EXAMPLE 7 Radiolabelling of5-(((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)carbonyl)-N,N,N-trimethylpyridin-2-aminiumTrifluoromethanesulfonate

5-(((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)carbonyl)-N,N,N-trimethylpyridin-2-aminiumTrifluoromethanesulfonate

Experimental:

Preparation of 1,1,1,3,3,3-hexafluoropropan-2-yl 6-chloronicotinate

To a stirred solution of 6-chloronicotinic acid (500 mg, 3.17 mmol) andN,N′-dicyclohexylcarbodiimide (DCC) (648 mg, 3.16 mmol) intetrahydrofuran (THF) (15 mL) was added1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP) (401 μL, 3.81 mmol) and acatalytic amount of 4-dimethylaminopyridine (DMAP). The mixture wasstirred for 48 h at room temperature. The organic phase was removed invacuo after which the solid residue was purified by silica gel flashchromatography (hexanes:ethyl acetate 1:1)1,1,1,3,3,3-hexafluoropropan-2-yl 6-chloronicotinate was obtained as acolourless solid (780 mg, 2.54 mmol).

Preparation of5-(((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)carbonyl)-N,N,N-trimethylpyridin-2-aminiumTrifluoromethanesulfonate

1,1,1,3,3,3-hexafluoropropan-2-yl 6-chloronicotinate (780 mg, 2.54 mmol)was dissolved in 5 ml dry THF after which was added 1 M trimethylaminesolution in THF (5.0 mL). A white precipitate was found 10 minutes afterthe reaction started, which was allowed to proceed overnight. Theprecipitate was collected and washed with cold Et20. The solid residuewas suspended in CH₂Cl₂, and TMSOTf (1 mL, 5.29 mmol) was added over 3minutes. The mixture was concentrated, and the residue wasrecrystallized from Et20 to afford5-(((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)carbonyl)-N,N,N-trimethylpyridin-2-aminiumtrifluoromethanesulfonate as a white solid (0.55 g, 45% yield).

Formation of5-(((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)carbonyl)-N,N,N-trimethylpyridin-2-aminiumtrifluoromethanesulfonate was confirmed by NMR:

¹H NMR (400 MHz, Acetonitrile-d₃) δ 9.22 (d, J=2.3 Hz, 1H), δ 8.74 (dd,J=8.8, 2.3 Hz, 1H), δ 8.03 (d, J=8.7 Hz, 1H), δ 6.46 (m, 1H), δ 3.58 (s,9H).

¹⁹F NMR (376 MHz, Acetonitrile-d₃) δ-73.72, δ-79.36.

Radiolabeling on solid phase of5-(((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)carbonyl)-N,N,N-trimethylpyridin-2-aminiumtrifluoromethanesulfonate

84.8 MBq of [¹⁸F]fluoride obtained from an aqueous solution was trappedon a Chromafix/Chromabond PS-CO3-anion exchange column (type shorty,MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany). The column wasimmediately rinsed with 2 mL of dry acetonitrile and purged with air (6mL with syringe) after which it was incubated at room temperature with a0.5 ml mixture containing 31.2 mg of5-(((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)carbonyl)-N,N,N-trimethylpyridin-2-aminiumtrifluoromethanesulfonate in 1:1 acetonitrile/t-BuOH for 2.5 minutesbefore the solution was pushed completely through the column manuallywith a syringe filled with air into an empty 3 ml glass vessel(receiving vial) and immediately analyzed by HPLC. The radioactivity inthe receiving vial was 48.4 MBq measured in a dose calibrator 10 minafter trapping of [¹⁸F]fluoride (84.8 MBq) on the column. Radio-HPLC(ACE 3 C18-50*4.6 mm, 10-90% acetonitrile over 10 min in water/0.05%TFA, 1 ml/min) of eluate showed a major radioactive peak eluting at7.893 min expected to be 1,1,1,3,3,3-hexafluoropropan-2-yl6-[¹⁸F]fluoronicotinate (¹⁸F-Py-HFIP).

¹⁸F-Py-HFIP (1,1,1,3,3,3-hexafluoropropan-2-yl-6-[¹⁸F]fluoronicotinate)

EXAMPLE 8

AG® MP-1M Anion Exchange Resins of mesh size 200-400 and 50-100 (each 42mg) were weighed out in two empty Chromafix columns (shortyMACHEREY-NAGEL GmbH & Co. KG, Dren, Germany) and converted from chlorideform to the HCO₃ ⁻ form by passing a 10 mL 1M KHCO₃ solution over theresins, followed by 10 mL Milli-Q water and then dried with air. 5 to 10MBq of [¹⁸F]fluoride obtained from an aqueous solution was trapped onthe AG resins.

The columns were immediately rinsed with 2 mL of dry acetonitrile andpurged with air (6 mL with syringe) after which they were incubated atroom temperature with a 0.5 ml mixture containing 22.94 mg ofN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate (1 eq.) precursor, 10 μL TEA (triethylamine)(1 eq.) in 1:1 acetonitrile/t-BuOH for 2 min and 30 seconds before thesolution was pushed completely through the column manually with asyringe filled with air into an empty 3 ml glass vessel (receiving vial)and immediately analyzed by radio-TLC and HPLC. Radio-HPLC showed amajor radioactive peak at 254 nm co-eluting with the reference standard,confirming identity, and radio-TLC showed 92.5% radiochemical yield of[¹⁸F]F-Py-TFP. The radiochemical yields and purities can be found inTable 6.

TABLE 6 BioRad polymer resin solid-phase labeling results of ¹⁸F-Py-TFPEntry A B C D E F G H I J K L 1 BioRad 30 C1 TEA 42.3 8.90 16:21 5.7616:31 76.8 65 49.8 AG- −10 μL MP-1M (200-400 mesh) 2 BioRad 30 C2 TEA43.6 5.04 16:54 1.70 17:02 28.9 34 9.9 AG- −10 μL MP-1M (50-100 mesh)Key to Table 6: A: Resin B: Precursor amount (mg) C: Solvent system (ml)C1: 1:1 t-BuOH/MeCN/0.5 C2: 1:1 t-BuOH/MeCN/0.5 D: Base E: Resin amount(mg) F: Start activity trapped on column (MBq)* G: Time start (hh:mm) H:Activity in receiving vial (MBq) I: Time end (hh:mm) J: RCY % byradio-TLC** K: Elution efficiency (%)*** L: Total yield no decaycorrected (%)**** *After rinsing column with MeCN **Mobile phase 100%MeCN (some hydrolysis of ester may occur during drying of TLC strip(silica), and actual yield may be under estimated depending on hold-uptime of sample on strip) ***Elution efficiency is not corrected fordecay and therefore slightly underestimated depending on time betweenmeasurements ****RCY by radio-TLC multiplied by elution efficiency

EXAMPLE 9

40.2 MBq of [¹⁸F]fluoride obtained from an aqueous solution was trappedon Chromafix/Chromabond PS-CO₃ ⁻ anion exchange column (type shorty,MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany). The column wasimmediately rinsed with 2 mL of dry absolute ethanol and purged with air(2 mL with syringe) after which it was incubated at room temperaturewith a 0.5 ml mixture containing 31.93 mg ofN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate (1 eq.) precursor, 10 μL DIEPA (1 eq.) in 1:1acetonitrile/t-BuOH for 2 min and 30 seconds before the solution waspushed completely through the column manually with a syringe filled withair into an empty 3 ml glass vessel (receiving vial) and immediatelyanalyzed by radio-TLC and HPLC. The radioactivity in the receiving vialwas 32.4 MBq measured in a dose calibrator 8 min after trapping of[¹⁸F]fluoride (39.6 MBq) on the column. Radio-HPLC showed a majorradioactive peak at 254 nm co-eluting with the reference standard,confirming identity, and radio-TLC showed 28% radiochemical yield of[¹⁸F]F-Py-TFP.

TABLE 7 Using 1 mL EtOH (abs.) replacing MeCN for removing water fromion-exchange cartridge after trapping ¹⁸F⁻ Entry A B C D E F G H I J K L1 Chromafix 31 C1 DIPEA 45 39.6 13:21 32.4 13:29 35 81.2 28 PS-CO3- −10μL anion exchange column (type shorty) Key to Table 7: A: Resin B:Precursor amount (mg) C: Solvent system (ml) C1: 1:1 t-BuOH/MeCN/0.5 D:Base E: Resin amount (mg) F: Start activity trapped on column (MBq)* G:Time start (hh:mm) H: Activity in receiving vial (MBq) I: Time end(hh:mm) J: RCY % by radio-TLC** K: Elution efficiency (%)*** L: Totalyield no decay corrected (%)**** *After rinsing column with EtOH**Mobile phase 100% MeCN (some hydrolysis of ester may occur duringdrying of TLC strip (silica), and actual yield may be under estimateddepending on hold-up time of sample on strip) ***Elution efficiency isnot corrected for decay and therefore slightly underestimated dependingon time between measurements ****RCY by radio-TLC multiplied by elutionefficiency

EXAMPLE 10

97.4 MBq of [¹⁸F]fluoride obtained from an aqueous solution was trappedon Chromafix/Chromabond PS-CO₃ ⁻ anion exchange column (type shorty,MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany). The column wasimmediately rinsed with 2 mL of dry acetonitrile and purged with air (2mL with syringe) after which it was incubated with a 0.5 ml mixturecontaining 31.93 mg ofN,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridin-2-aminiumtrifluoromethanesulfonate (1 eq.) precursor, 10 μL TEA (1 eq.) in 1:1acetonitrile/t-BuOH for 2 min and 30 seconds simultaneously using a heatgun blowing hot air over the cartridge (60-70° C. at surface ofcartridge) before the solution was pushed completely through the columnmanually with an air filled syringe into an empty 3 ml glass vessel(receiving vial) and immediately analyzed by radio-TLC and HPLC. Theradioactivity in the receiving vial was 72.4 MBq measured in a dosecalibrator 11 min after trapping of [¹⁸F]fluoride (93.9 MBq) on thecolumn. Radio-HPLC showed a major radioactive peak at 254 nm co-elutingwith the reference standard, confirming identity, and radio-TLC showed92% radiochemical yield of [¹⁸F]F-Py-TFP.

TABLE 8 With heating using heatgun a 5 cm distance over column for 3 min(60-70 C.°) Entry A B C D E F G H I J K L 1 Chromafix 30 C1 DIPEA 4593.9 00:00 74.2 00:11 92 79 72.7 PS-CO3- −10 μL anion exchange column(type shorty) Key to Table 8: A: Resin B: Precursor amount (mg) C:Solvent system (ml) C1: 1:1 t-BuOH/MeCN / 0.5 D: Base E: Resin amount(mg) F: Start activity trapped on column (MBq)** G: Time start (hh:mm)H: Activity in receiving vial (MBq) I: Time end (hh:mm) J: RCY % byradio-TLC** K: Elution efficiency (%)*** L: Total yield no decaycorrected (%)****

EXAMPLE 11 Synthesis and radiolabelling of1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumtrifluoromethanesulfonate

Synthesis

To a stirred solution of 2,3,5,6-tetrafluorophenyl 6-chloronicotinate(500 mg, 2.54 mmol) in 5 ml dry THF was added 1 mL ofN-methylpyrrolidine. A white precipitate started to form after 10 minand reaction was allowed to proceed overnight. The precipitate wascollected and washed with cold Et20. The solid residue was suspended inCH₂Cl₂, and TMSOTf (1 mL, 5.29 mmol) was added over 3 min. The mixturewas concentrated, and the residue was recrystallized from Et20 to afford1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumtrifluoromethanesulfonate as a white solid (0.70 g, 55%)

¹H NMR (400 MHz, Acetonitrile-d₃) δ 9.32 (dd, J=2.3, 0.8 Hz, 1H), δ 8.83(dd, J=8.7, 2.3 Hz, 1H), δ 8.01 (dd, J=8.7, 0.8 Hz, 1H), δ 7.43 (m, 1H),δ 4.23 (m, 2H), δ 4.01 (m, 2H), δ 3.46 (s, 3H), 2.34 (m, 2H), 2.24 (m,2H).

¹⁹F NMR (376 MHz, Acetonitrile-d₃) δ-79.36 (s), 6-140.36 (m), 6-154.41(m).

Radiolabelling:

49.5 MBq of [¹⁸F]fluoride obtained from an aqueous solution was trappedon a Chromafix/Chromabond PS-CO3-anion exchange column (type shorty,MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany). The column wasimmediately rinsed with 2 mL of dry acetonitrile and purged with air (6mL with syringe) after which it was incubated at room temperature with a0.5 ml mixture containing 30.24 mg1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumtrifluoromethanesulfonate and 10 μL triethylamine in 1:1acetonitrile/t-BuOH for 2.5 minutes before the solution was pushedcompletely through the column manually with a syringe filled with airinto an empty 3 ml glass vessel (receiving vial) and immediatelyanalyzed by HPLC. The radioactivity in the receiving vial was 23.0 MBqmeasured in a dose calibrator 14 min after trapping of [¹⁸F]fluoride(49.5 MBq) on the column. Radio-HPLC (ACE 3 C18-50*4.6 mm, 10-90%acetonitrile over 10 min in water/0.05% TFA, 1 ml/min) of the eluateshowed a major radioactive peak co-eluting with F-Py-TFP referencestandard at 7.890 min.

EXAMPLE 12

Radiosynthesis of [¹⁸F]DCFPyL was carried out according to the protocoldescribed below and illustrated in Scheme 1.

PSMA precursor (Glu-CO-Lys) was obtained from ABX GmBH (Germany).

[¹⁸F]F-Py-TFP synthesized “on-cartridge” was purified by diluting thedownstream eluate (500 μL) with 5 mL 10% AcOH and trapped on a tC18Sep-Pak Plus cartridge. The cartridge was washed with water (10 mL), anddried with helium-flow. [¹⁸F]F-Py-TFP was eluted off the C₁₈ cartridgewith diethyl ether (2 mL) simultaneously passing the eluate through anNa₂SO₄ drying cartridge (Sep-Pak plus long, Waters). The diethyl etherwas removed using a helium sweep gas. The purified [¹⁸F]F-Py-TFP wasreconstituted in 500 μL acetonitrile.

To two separate glass vials each containing 1 mg PSMA (Glu-CO-Lys)precursor in 222 uL DMSO was added 2 μL TEA followed by 100 μL ofradiochemical pure [¹⁸F]F-Py-TFP (90 MBq) in MeCN. Reaction was allowedto proceed for 1 h (vial 1) at room temperature and 10 min at 65° C.(vial 2). Radio-HPLC indicated 89% (vial 1) and 85% (vial 2) conversionto [¹⁸F]DCFPyL. Radiolabeled products co-eluted with an authentic DCFPyLreference sample (R_(T)=3.257 min). Radio-HPLC (ACE 3 C18-50*4.6 mm, 10%ACN in H₂O/0.05% TFA isocratic, 5 min, then to 95% ACN over 9 min, 1ml/min).

EXAMPLE 13

[¹⁸F]MEL050 was Synthesised from N,N-diethyleneethylenediamine and¹⁸F-Py-TFP According to the Protocol Described Below and Illustrated inScheme 2:

MEL050 Synthesis (Reference Standard):

2-(diethylamino)-ethyl)-6-fluoronicotinamide (MEL050) was synthesizedand characterized according to the method described in Greguric, I, etal. Journal of Medicinal Chemistry 2009 52 (17), 5299-5302, accessibleat DOI: 10.1021/jm9008423, the entire contents of which are incorporatedherein by reference.

[¹⁸F]Mel050 Synthesis:

21.21 MBq of aqeuous fluoride-18 was trapped on Chromafix PS-HCO₃cartridge (type shorty, MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany).The column was immediately rinsed with 2 mL of dry acetonitrile andpurged with air (6 mL with syringe) after which it was incubated at roomtemperature with a 0.5 ml mixture containing 27.6 mg1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-iumtrifluoromethanesulfonate, 10 μL triethylamine in 1:1acetonitrile/t-BuOH (500 μL) for 2.5 minutes before the solution waspushed manually and completely through the column with a syringe filledwith air into an empty 3 ml glass vessel (receiving vial). Theradioactivity in the receiving vial was 16.8 MBq measured in a dosecalibrator 8 min after trapping of [¹⁸F]fluoride (22.21 MBq) on thecolumn.

10 μL N,N-diethyleneethylenediamine was added directly to the receivingvial containing the [¹⁸F]F-Py-TFP eluate, reacted for 5 min at roomtemperature and analyzed by radio-TLC and radio-HPLC to verify identity(by co-elution with reference standard) and radiochemical yield.Radio-HPLC and TLC indicated full conversion from [¹⁸F]F-Py-TFP to[¹⁸F]MEL050. Free fluoride-18 was removed by trapping the radioactiveproduct after diluting the reaction mixture with water (1:20), loadingit onto an Oasis MCX plus cartridge (Waters) followed by a water rinse(5 ml). 7.55 MBq of product was retained on the Oasis MCX plus (Waters)27 minutes after start of synthesis. A mixture of 5% acetic acid withtrimethylamine in water/ethanol (1:1) eluted off radiochemical pure[¹⁸F]MEL050 (>99% radiochemical purity) in which co-eluted with anauthentic reference sample of MEL50 (R_(T)=3.53 min). Radio-HPLC (ACE 3C18-50*4.6 mm, 3-40% acetonitrile over 10 min in water/0.05% TFA, 1ml/min).

EXAMPLE 14

[¹⁸F]F-Py-TFP is prepared as described herein and then reacted withbiomolecules of general formula (C) in which n is 1, 2, 3, 4, 5, 6, 7, 8or 9. The reaction is carried out in the presence of TEA and DMSO atroom temperature for 1 hour, or at 65° C. for 10 minutes. In analternative approach the reaction is carried out in the presence oftetraethylammonium bicarbonate and ethanol at 40° C. for 3 minutes.

[18F]DCFPyL (where n=4) and analogues with n=1, 2, 3, 5, 6, 7, 8 and 9are obtained.

1-29. (canceled)
 30. A compound of formula (I′) or formula (I″), or asalt thereof:

wherein L is a positively charged leaving group selected from —N(C₁₋₆alkyl)₃ ⁺, 1,4-diazabicyclo[2.2.2]octan-1-ium, and 1-(C₁₋₃alkyl)-pyrrolidin-1-ium; R′ is an electron-withdrawing group; and L′ is1,4-diazabicyclo[2.2.2]octan-1-ium or 1-(C₁₋₃ alkyl)-pyrrolidin-1-ium.31. The compound of claim 30, which is a compound of formula (I′) or asalt thereof.
 32. The compound of claim 30, which is a compound offormula (I″) or a salt thereof.
 33. The compound of claim 30, wherein R′is —CF₃, —CH₂CF₃, —CH(CF₃)₂, —C(CF₃)₃, or

where n is an integer from 1 to 5 and each Z is independently —F, —Cl,—NO₂, or —CN.
 34. The compound of claim 30, wherein R′ is

where n is an integer from 1 to 5 and each Z is independently —F, —Cl,—NO₂, or —CN.
 35. The compound of claim 30, which is a compound offormula (I^(n)):

where n is an integer from 1 to 5 and each Z is independently —F, —Cl,—NO₂, or —CN.
 36. The compound of claim 30, which is a compound ofgeneral formula (I^(s)):

wherein L′ and R′ in said compound of general formula (I^(s)) areselected such that said compound is one of compounds (8) to (21): R′ L′

(8) (9) (10) (11) (12) (13) (14)

(15) (16) (17) (18) (19) (20) (21).


37. The compound of claim 30, which is in the form of atrifluoromethanesulphonate salt.
 38. The compound of claim 30, which is5-formyl-N,N,N-trimethylpyridin-2-aminium trifluoromethanesulfonate. 39.The compound of claim 30, which is1-methyl-1-(5-((2,3,5,6-tetrafluorophenoxy)carbonyl)pyridin-2-yl)pyrrolidin-1-ium trifluoromethanesulfonate.